Locus of Points / Envelope

Locus of Points / Envelope

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Locus_Construction 

You can construct a locus of points or envelope from a selected point or line, by defining a range for some constraint in the drawing. Just follow these easy steps:

  1. Select ebd_Ebd179  the point on the drawing that will form the locus (point B in the example below); select a line, line segment, or vector to form an envelope.
  2. When you click the Locus icon ebd_Ebd180  , the Edit Locus dialog pops up.

edit locus 1 

3.  You need a parameter to drive the motion to create the locus. Click the arrow key to the right of the Parametric Variable window to select from a list of all variables in the drawing. (If you entered the needed constraint in real terms, Cancel the trace and change the constraint to a variable by double-clicking it in the drawing window.)

edit locus 2 

4.  Simply fill in the values for the appropriate variable and click the Ok button.

ebd_Ebd183 

warning  Note: The locus only works if the figure's position is fixed i.e. a point in a triangle will not work as a locus unless the location of the other two points are fixed with coordinate constraints.

To adjust the range of the locus, double-click the locus to edit the dialog.

The following example shows an envelope of the line DE. We use the Point proportional along curve constraint and the parameter t to position the points D and E (D is (1-t) along line AC and E is t along line AB). In the Edit Locus dialog, we create the envelope from parameter t as it ranges from 0 to 1.

Locus_Example 

You can replay the creation of the envelope with the Animation tools. Select variable t and click the Play button.